Fuel Injection

ABSTRACT

A fuel injector ( 1 ) for fuel-injection systems of internal combustion engines has a nozzle body ( 2 ) and a magnetic coil ( 3 ) positioned in a magnetic cup ( 6 ), the magnetic coil ( 3 ) being penetrated by the nozzle body ( 2 ); and a plastic coating ( 8 ) which at least partially surrounds the nozzle body ( 2 ). The nozzle body ( 2 ) and the magnetic cup ( 6 ) are sealed from an environment of the fuel injector ( 1 ) by a thread-type labyrinth seal ( 5 ).

BACKGROUND INFORMATION

[0001] The present invention is directed to a fuel injector of the typeset forth in the main claim.

[0002] From DE 198 49 210 A1, for example, a fuel injector is knownwhich has a nozzle body that has a tubular design at its downstreamside, and at whose downstream end a sealing seat and a discharge orificeare located. The tubular section of the nozzle body can be inserted intoa receiving bore of a cylinder head. The nozzle body is sealed from thereceiving bore of the cylinder head, which has a diameter thatcorresponds to the radial extension of the nozzle body, by a seal havingapproximately the geometry of a hollow cylinder.

[0003] For fixing the seal in position on the nozzle body, the nozzlebody is provided with a circumferential groove into which the seal isinserted, the groove being introduced, for example, by desurfacing thenozzle body. To be used as materials are elastic materials which, forinstallation in the groove, can be slipped over the nozzle body.

[0004] Moreover, from DE 198 08 068 A1, as well, a fuel injector isknown in which a sealing element is positioned on the nozzle body. Theseal is made of a metallic material and expands in the radial directionunder the influence of the temperature generated by the combustionprocess. This may be achieved either by a shape-memory alloy or by theuse of a bi-metal seal. As in DE 198 49 210 A1, a groove in the nozzlebody may be used for the fixation.

[0005] During operation of the internal combustion engine, the metalsealing ring heats up and expands, thereby increasing the sealing effectduring operation. To facilitate the installation, the metal seal has aslightly smaller diameter than the receiving bore introduced in thecylinder head for the fuel injector.

[0006] A primary disadvantage of the sealing approach proposed in DE 19849 210 A1 is the high temperature to which the seal is exposed.Especially in directly injecting internal combustion engines ahigh-speed resistance of non-metallic sealing materials cannot beensured.

[0007] The fuel injector described in DE 198 08 068 A1 has thedisadvantage that the sealing effect of the metallic seal istemperature-dependent. Following a cold start of the internal combustionengine, some time elapses before the combustion process heats up thematerials in the vicinity of the combustion chamber to such a degreethat, due to heat conduction, the temperature leading to the requireddeformation is achieved in the seal. For this reason, another seal isrequired, in addition to the mentioned seal, in order to seal thecombustion chamber from the external space at the start of operation ofthe internal combustion, in order not to lose any compression pressure.

[0008] Also disadvantageous are the costly materials that are used inthe production of metal seals that deform as a function of temperature.A shape-memory alloy has a transition temperature that is adapted to theintended application. In order to reliably ensure this transitiontemperature, a narrow range is often required for the manufacturingprocess. This not only causes an increase in the development costs forthe alloy but also raises the cost when used in series production.

[0009] The use of a bimetal seal requires the seal to be affixed on thenozzle body which serves as a counter bearing in the deformation.However, installing the bimetal in a groove, for instance, is difficultsince the properties of the material change when one of the two metalsundergoes non-elastic deformation during installation.

SUMMARY OF THE INVENTION

[0010] In contrast, the fuel injector according to the present inventionhaving the characterizing features of the main claim has the advantageover the related art that the nozzle body and a magnetic cup in whichthe magnetic circuit of the fuel injector is encapsulated, are sealedfrom an environment of the fuel injector by a thread-type labyrinthseal.

[0011] Advantageous further refinements of the fuel injector configuredaccording to the present invention are possible by using the measuresrecited in the dependent claims.

[0012] The labyrinth seal advantageously has two to three threads whichhave a radial amplitude of approximately 0.5 mm so as to obtain areliable sealing effect.

[0013] Furthermore, it is advantageous that the labyrinth seal is ableto be produced in a simple manufacturing process, using a threading toolor an internal mandrel, without reworking by cutting being required.

[0014] An additional advantage is that the form of the thread is notlimited to round cross sections but may be produced as desired in anelliptical form or as an oval.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] An exemplary embodiment of a fuel injector configured accordingto the present invention is represented in simplified form in thedrawing and is elucidated in greater detail in the followingdescription.

[0016] The figures show:

[0017]FIG. 1 a schematic part-sectional view through an exemplaryembodiment of a fuel injector configured according to the presentinvention;

[0018]FIG. 2 a cutout from the exemplary embodiment, represented in FIG.1, of a fuel injector 1 configured according to the present invention,in area II in FIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0019] A fuel injector 1, represented in FIG. 1, is configured in theform of a fuel injector for fuel-injection systems ofmixture-compressing internal combustion engines with externally suppliedignition. Fuel injector 1 is particularly suited for the directinjection of fuel into a combustion chamber (not shown) of an internalcombustion engine.

[0020] Fuel injector 1 includes a sleeve-shaped nozzle body 2 in which,for instance, a valve needle (not shown further) may be positioned. Fuelinjector 1 in the exemplary embodiment is an electromagneticallyactuated fuel injector. Nozzle body 2 penetrates a magnetic coil 3 whichis wound onto a coil brace 4. Magnetic coil 3 is encapsulated in amagnetic cup 6 which is sealed from a surrounding of fuel injector 1 bya labyrinth seal 5 configured according to the present invention.

[0021] A detailed representation of labyrinth seal 5 of fuel injector 1configured according to the present invention may be gathered from FIG.2 and the following description.

[0022] Magnetic coil 3 is energized via an electric line (not shownfurther) by an electric current, which may be supplied via an electricalplug contact 7. A plastic coating 8, which may be extruded onto nozzlebody 2, encloses plug contact 17.

[0023]FIG. 2, in a part-sectional view, shows the area designated II inFIG. 1, from the exemplary embodiment of a fuel injector 1 designedaccording to the present invention, as represented in FIG. 1.

[0024] As already mentioned, magnetic coil 3 and nozzle body 2 of fuelinjector 1 configured according to the present invention are providedwith a labyrinth seal 5 which seals the components enveloped by plasticcoating 8 from the environment of fuel injector 1 and, thus, protectsthem from dirt and salt water, for example.

[0025] Labyrinth seal 5 has a threaded design and includes at least two,but better three thread grooves 9. A radial distance between a low point10 of each thread groove 9 and a high point 11 of each thread grooveshould amount to at least 0.5 mm.

[0026] The form of the thread may be arbitrary. Easiest to produce is around thread, but elliptical cross sections are also conceivable.

[0027] Labyrinth seal 5 is inserted in order to protect the regionsurrounded by plastic coating 8, including nozzle body 2, fromaggressive media in the vicinity of fuel injector 1. A labyrinth seal 5,having a thread-type design as in fuel injector 1 according to thepresent invention, allows for a rotary release of the tool that produceslabyrinth seal 5, thereby dispensing with reworking, and simplifying theproduction process which becomes less cost-intensive as a result.

[0028] Labyrinth seal 5 is able to be produced, for instance, bydeep-drawing or extruding, thread grooves 9 being produced by athread-cutting tool. A thread-type labyrinth seal 5 may also be formedby rotary swaging or round kneading with the aid of a thread-typeinternal mandrel.

[0029] The present invention is not restricted to the exemplaryembodiment of a fuel injector 1 configured according to the presentinvention as shown, but is suited for various design of fuel injectors1.

What is claimed is:
 1. A fuel injector (1) for fuel-injection systems ofinternal combustion engines having a nozzle body (2) and a magnetic coil(3) positioned in a magnetic cup (6), the magnetic coil (3) beingpenetrated by the nozzle body (2), and having a plastic coating (8)which at least partially surrounds the nozzle body (2), wherein thenozzle body (2) and the magnetic cup (6) are sealed from an environmentof the fuel injector (1) by a thread-type labyrinth seal (5).
 2. Thefuel injector as recited in claim 1, wherein the labyrinth seal (5)includes at least two thread grooves (9).
 3. The fuel injector asrecited in claim 2, wherein a radial distance between a radially innerlow point (10) and a radially outer high point (11) of the threadgrooves (9) is at least 0.5 mm.
 4. The fuel injector as recited in oneof claims 1 through 3, wherein the labyrinth seal (5) is produced bydeep-drawing, extruding or rotary swaging.
 5. The fuel injector asrecited in claim 4, wherein the thread grooves (9) of the labyrinth seal(5) are produced by a thread-cutting tool or a thread-type internalmandrel.
 6. The fuel injector as recited in one of claims 1 through 5,wherein the thread grooves (9) have a round, an oval or an ellipticalcross section.